High-speed digital printing presents unique requirements to data-processing equipment. For example, to operate a printing apparatus which is designed to output over 100 page-size images per minute, the ability to make the desired image data to print a particular page available to the printing hardware requires very close tolerances in the management of the "overhead" when data is transferred from a memory and applied to the printing hardware. A typical letter-sized page image at 600 spi resolution, in a format suitable to be submitted to printing hardware, is typically of a size of about 4MB; when printing hardware demands the image data to print the particular page image, this 4 MB image data must be accessed from memory within a time frame of approximately 300 milliseconds.
As is known in the art of digital printing, these large quantities of data must be processed in numerous sophisticated ways. For example, image data in a page description language (PDL), such as HP-PCL or PostScript.TM., must be decomposed into raw digital data, and this raw digital data may often have to be compressed and decompressed at least once before the data reaches the printing hardware. In addition, in a high-volume situation where hundreds of different pages are being printed in various jobs, the particular set of image data corresponding to a page to be printed at a given time-window must be carefully managed.
Adobe.RTM. Corporation, creator of the "PostScript.TM." page description language, has developed a system, generally known by the trademark "Extreme.TM.," which enables what can be called "page-parallel" decomposition of page images to be sent to printing apparatus. In brief, the "Extreme" concept involves taking a multi-page job, which may be originally in the PostScript PDL, and as a first step converting the PostScript image into a "portable document format" file or PDF. The advantage of the portable document format file is that it is page-independent: a multi-page document converted into a PDF can readily be divided into subsets of data, each subset of data corresponding to one of the multiple page images in the job or document. The Extreme architecture exploits the page-independence of PDF by being able to divide the data for a multi-page document readily into component subsets, each subset corresponding to one page of the document, and sending a plurality of such page images to multiple decomposers simultaneously. In this way, a number of individual page images in a multi-page document can be decomposed in parallel, thus sharply reducing the amount of time required to decompose an entire multi-page document.
The network printing system marketed by Xerox Corporation under the trademark DocuSP.TM., or "Document Services Platform," the basic functionality of which is described in detail in the patent incorporated by reference above, is a system which allows a relatively large population of users on a network to submit jobs at random times to a high-speed (such as 180 ppm) printing apparatus. In brief, DocuSP uses a plurality of independent decomposers, which may be for different PDL's, such as PostScript or PCL, and directs jobs coming in over the network to the appropriate decomposer. DocuSP uses what is called a "buffer manager" to keep track of individual page images as they emerge at random times from different decomposers. Then, decomposed images from various users can be retained in memory until the precise time-window in which a particular page image for a particular job is output by the high-speed digital printing apparatus.
The present invention is basically an arrangement by which the page-parallel decomposing of Adobe Extreme system can be integrated with the high-speed, multi-user model of DocuSP.